1. Field of the Invention
The present invention relates to a routing method, and especially to a method for optimizing packet delivery between two mobile stations (MSs) in packet radio networks.
2. Description of the Related Art
Wireless mobile communication has developed rapidly in recent years. A new requirement for the third generation is to carry out roaming functions. The roaming content can include not only voice but also video and data transmission, requiring wideband data communication capability. Also important is connection to existing networks by method of a third generation cellular phone to utilize available resources. For this purpose, mobile communication networks are combined with fixed data communication networks. The Internet protocol (IP) is defined for communication between mobile communication networks and fixed data communication networks to play an important role in switching data, video, multimedia information and so on.
IP adopts packet switching in data processing and therefore wireless communication protocol with packet switching such as General Packet Radio Service (GPRS) and Universal Mobile Telecommunication System (UMTS) has been developed. The cited packet radio networks defined by the wireless communication protocol replace circuit switching in conventional data processing with packet switching such that mobile stations (MSs) can go online to the Internet and communicate with hosts connected to the Internet. For embodied explanation of packet radio networks, a GPRS example is given in the following.
FIG. 1 is a schematic diagram of a typical GPRS Public Land Mobile Network (PLMN) architecture and packet delivery path for a communication between an MS and the Internet host (i.e., a MS-to-Host communication). In FIG. 1, the network 100 includes Gateway GPRS Support Node (GGSN) 12, Serving GPRS Support Nodes (SGSNs) 14a˜14c, base station subsystems (BSSs) 16a-16g and mobile station (MS) 18, wherein GGSN 12 is an interface between the Internet 110 and the network 100. MS 18 can have bidirectional communication with the host 20 on the Internet 110. When MS 18 has data packets to the host 20, MS 18 must connect to the network 100 first. Thus, SGSN 14a in the network 100 can record a current position message of MS 18 and receive and forward data packets between MS 18 and GGSN 12. GGSN 12 can deliver packets forwarded by SGSN 14a to external networks with TCP/IP protocol. As an example, packets here are forwarded to the host 20 on the Internet 110. Also, when the host 20 on the Internet 110 has packets to MS 18, the packets are forwarded from the Internet 110 to SGSN 14a in GPRS 100 through GGSN 12 and further forwarded from SGSN 14a to MS 18 through BSS 16a. 
According to GPRS protocol structure, GGSN is the first node understanding the Internet Protocol (IP) of the MS-to-Host communication. In other words, GGSN 12 in this example is the first hub for every packet regardless of packet destination. Therefore, every packet from MS 18 must go to GGSN 12 first. Considering a GPRS may provide mobile station-to-mobile station packet service, that is, MS-to-MS communication, the destination of packets may be in the same base station subsystem (BSS) or SGSN. The former is shown in FIG. 2a and the latter is shown in FIG. 2b. 
FIG. 2a is a schematic diagram of the MS-to-MS communication when two MSs are in the same BSS. In FIG. 2a, GPRS 100 includes GGSN 12, SGSNs 14a˜14c, BSSs 16a˜16g and MSs 18a˜18b, wherein GGSN 12 is an interface between the network 100 and the Internet 110 for providing communication between the host 20 on the Internet 110 and MSs 18a˜18b in the network 100.
As shown in FIG. 2a, MSs 18a and 18b connect to the network 100 through BSS 16a in order to communicate with each other. When MS 18a has a packet to MS 18b, MS 18a forwards the packet, through BSS 16a, to SGSN 14a and to GGSN 12. Next, GGSN 12 forwards the packet to MS 18b through SGSN 14a and BSS 16a. Similarly, when MS 18b has a packet to MS 18a, a delivery path is from MS 18b to MS 18a through BSS 16a, SGSN 14a, GGSN 12, SGSN 14a and BSS 16a. A GPRS routing design as cited lacks efficiency.
FIG. 2b is a schematic diagram of the MS-to-MS communication when two MSs are in the same SGSN but different BSSs. In FIG. 2b, the architecture of GPRS 100 is similar to FIG. 2a except that MSs 18a and 18b connect to the network 100 through different BSSs 16a and 16c, respectively in the same SGSN 14a. As shown in FIG. 2b, when MS 18a has a packet to MS 18b, MS 18a forwards the packet, through BSS 16a, to SGSN 14a and to GGSN 12. Next, GGSN 12 forwards the packet, through SGSN 14a, to BSS 16c and to MS 18b. Similarly, when MS 18b has a packet to MS 18a, a delivery path is from MS 18b to MS 18a through BSS 16c, SGSN 14a, GGSN 12, SGSN 14a and BSS 16a. Obviously, this GPRS routing design also lacks efficiency.
FIG. 2c is a schematic diagram of the MS-to-MS communication when two MSs are in different SGSNs. In FIG. 2c, the architecture of GPRS 100 is similar to FIG. 2a except that MSs 18a and 18b are serviced by different SGSNs 14a and 14b. MS 18a connects to the network 100 through BSS 16a and is serviced by SGSN 14a. MS 18b connects to the network 100 through BSS 16d and is serviced by SGSN 14b. As shown in FIG. 2c, when MS 18a has a packet to MS 18b, MS 18a forwards the packet, through BSS 16a, to SGSN 14a and to GGSN 12. Next, GGSN 12 forwards the packet, through SGSN 14b, to BSS 16d and to MS 18b. Similarly, when MS 18b has a packet to MS 18a, a delivery path is from MS 18b to MS 18a through BSS 16d, SGSN 14b, GGSN 12, SGSN 14a and BSS 16a. Again, this path lacks efficiency.
Accordingly, the above-cited designs for delivery paths are not optimized based on GPRS because all packet delivery has to pass through GGSN 12, decreasing the overall performance of the GPRS networks and introduces end-to-end delay for MS-to-MS communications.